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	<h1>:: Reference :: Constant Sizes ::</h1>

	Constant sizes are used to set the size of gaps 
	and other fixed layout elements. They can also be used
	in bounded sizes as lower or upper bound.


	<h2>Units</h2>
		
	Constant sizes are specified by a value plus unit that is one of: 
	<i>Pixel, Points, Inches, Millimeter, Centimeter</i> and <i>Dialog Units</i>.
	In string representations the units are abbreviated as: 
	<i>px, pt, in, mm, cm</i> and <i>dlu</i>.
	
	
	<h2>Constant Non-Pixel Sizes</h2>
	
	Constant sizes are constant for a given dialog font, font size and screen resolution. 
	Pixel sizes map to a fixed dimension in pixels - even if these 
	parameters change. This is undesired in screen design, especially
	in multi-platform environments.
	Therefore you should favor non-pixel sizes over pixel sizes.
		
	<p>
	If you move an application from Windows to Mac or Linux, you want
	to retain the overall appearance and layout propertions. 
	And if you just change your Windows desktop font settings,
	you want all layout elements grow appropriately: labels, fields,
	buttons, but also: gaps, borders, minimum sizes and dialog dimensions. 
	
	<p>
	Layout managers have been designed to address this issues. 
	Nevertheless, most of them fail to retain proportions
	if you specify dimensions in pixel, which is often the case
	for gaps, borders, dialog sizes, and custom minimum and preferred sizes.
	
	<p>
	For example, a well designed OK button shall have a minimum width;
	75px is appropriate for an 8pt Tahoma font on Windows with 96dpi.
	But on 120dpi and 10pt Arial, 75 pixels are perceived
	as quite narrow. 
	
	<i>Dialog Units</i> allow to specify such a size
	in a way that it grows and shrinks with the environment. For example,
	the MS layout style guide suggests a command button minimum width 
	of 50dlu, which maps to 75px in the first context and to 100px in the second.
	
	<p><i>Points, Inches, Millimeters</i> and <i>Centimeters</i>
	are intended for sizes that shall grow with the screen resolution 
	but that are independent of the font and font size.
	
	
	<h2>Unit Conversion</h2>
	
	Class <tt>Sizes</tt> provides methods to convert non-pixel sizes 
	to pixels. The actual mapping is performed by a customizable
	<i>Unit converter</i>.	 
	
	
	<h2>Prototype Sizes</h2>
	
	You can describe a column width or row height by providing a
	string prototype, for example 
	<tt>new FormLayout("right:pref, 3dlu, '+49-89-32168'")</tt>.
	Prototype sizes scale better than <i>Dialog Units</i> if
	the content consists only of special characters, for example digits. 
		
	
	<h2>Logical Constant Sizes</h2>
	
	Logical sizes can be used to specify a size that changes
	with the current platform or style guide. 
	For example, if you want to specify a button's minimum width,
	you may want to use <i>50dlu</i> on Windows and <i>68px</i> on a Mac.
	Or you define the gap between two related text field rows
	as <i>3dlu</i> on Windows and <i>4px</i> on a Mac.
	
	<p>
	The Forms layout system supports logical sizes in builder
	classes, via the <i>Layout Style</i> and the <tt>FormFactory</tt> 
	constants.
	Since version 1.2 you can use logical sizes in encoded
	column and row specifications too, by means of layout variables.
	For example <tt>new FormLayout("right:pref, $lcgap, pref")</tt>
	uses the short name of the variable	<tt>$label-component-gap</tt>
	that describes the platform-specific gap between a label and
	its associated component. 

	<p>
	The <tt>ButtonBarFactory</tt>, <tt>ButtonBarBuilder</tt> and 
	<tt>ButtonStackBuilder</tt>
	use logical sizes and in turn style guide-specific logical sizes 
	for frequently used gaps and minimum widths and heights.
	For example the <tt>ButtonBarBuilder</tt> uses logical sizes 
	to honor style guide settings for button minimum width, and gaps 
	between related and unrelated components. 
	
	<p>
	If you develop a custom builder class, you can refer to the
	logical sizes using the current <i>Layout Style</i> or 
	the <tt>FormFactory</tt> constants.
	
	
	<h2>String Representations</h2>
	
	I recommend to specify column and row sizes in 
	the FormLayout constructor using string representations.
	These strings will be accepted by the <tt>FormLayout</tt>,
	<tt>ColumnSpec</tt>, <tt>RowSpec</tt> and <tt>Borders</tt> classes.
	
<pre>
constantSize ::= <integer>integerUnit | <double>doubleUnit
integerUnit  ::= PX | PT | DLU
doubleUnit   ::= IN | MM | CM
</pre>


	<h2>Examples</h2>
	
<pre>
new ColumnSpec("50dlu");
new ColumnSpec("75px");
new ColumnSpec("'xxx-MMM-000-xxx'");

new RowSpec("2in");
new RowSpec("100px");

new FormLayout("100dlu, 4dlu, 200dlu", 
               " 14dlu, 3dlu,  14dlu");
</pre>	




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